ORDOVICIAN GEODYNAMICS: Sardic Phase in the Pyrenees, Mouthoumet and Montagne Noire massifs: Field Trip

Fieldtrip throughout the Eastern Pyrenees and the Mouthoumet and Montagne noire massifs, Catalonia and Occitanie

• 6th September – Fieldtrip to eastern Pyrenees, Catalonia.

STOP 6a. Ribes granophyre (458±3 Ma): an undeformed, fine-grained, leucocratic granitic body with a microscopic granophyric texture crops out at the base of the Upper Ordovician along the Sardic unconformity that separates the Upper Ordovician from underlying Ediacaran–Lower Ordovician metasediments. Although it is locally affected by faults along the contact with the host rocks, it is possible to observe intrusive to concordant contacts, suggesting a laccolithic emplacement for this subvolcanic body.

STOP 6b. Surroundings of Ribes de Freser: Upper Ordovician volcanism. Lithic-rich, partially welded ignimbrite of dacitic composition (Pyroclastic Density Current) is interbedded in the upper part of the Upper Ordovician succession. The deposits are characterized by a high content in lithic clasts of small size (< 1 cm) and lapilli-sized flattened pumices (fiammes) completely devitrified and transformed into chlorite and clay minerals. The presence of these materials in the Upper Ordovician succession indicates a highly explosive subaerial felsic volcanism coeval with detrital sedimentation.

STOP 6c. Ribes-Bruguera road: Upper Ordovician limestones. The Upper Ordovician limestones attain a maximum thickness along the roads close to Bruguera and El Baell, south of Ribes. Three different limestone levels can be recognized in a 300 m-thick succession made up of limestones and marly-limestones (“schistes troués”).

Encrinitic packstone.

Echinoderm-bryozoan floatstones representative of
meadows affected by storm-induced processes.

Section of a Rhynchonelliformean brachiopod.

Encrinitic packstone containing articulated echinoderm columnals.

Section of a gastropod with calcitic cement.

Top of El Baell Formation, at stratotype, with karstic contact
with Hirnantian black shales of the Ansovell Formation.

STOP 6d. The Upper Ordovician unconformity at La Molina station (optional, depending on fieldtrip schedule): Upper Ordovician unconformity marked by the reddish-purple, unfossiliferous, conglomerates of the la Rabassa Formation. A synsedimentary hydrothermal activity is related to development of normal faults giving rise to quartz veins incorporated as quartz pebbles in the conglomerates.

Clasts of the Rabassa Formation composed of polyphasic
fragments of slates, sandstones and hydrothermal quartz
(La Molina locality).

Hydrothermal quartz dyke lining the

synsedimentary fault of a half-graben
infilled with quartz-rich conglomerates
(Rabassa Formation) sourced from the

dykes (La Molina locality).

• 7th September – Fieldtrip to eastern Pyrenees, Occitanie.

STOP 7a. The Upper Ordovician succession north of Bellver (Talltendre area): five formations can be recognized across the area exhibiting some lithologic variations, which broadly constitute a fining-upward sequence with an interlayered limestone key level and marked thickness variations between 100 and 1000 m related to synsedimentary faulting activity.

Low-angle conglomerates of the Rabassa Formation.

Angular discordance between vertical shale/sandstone
alternations of the Jujols Group.

Hydrothermal quartz dyke lining the synsedimentary fault
of a half-graben infilled with quartz-rich conglomerates
(Rabassa Formation) sourced from the dykes.

Trough cross-stratified sets and channels of conglomerates
and sandstones marking the uppermost part of the
Rabassa Formation.

STOP 7b. Graus de Canaveilles along the Conflent valley: classical stop with old model involving a “Cadomian” granitic basement (Carança orthogneiss) “overlain” by the Canaveilles Series. This model was ruled out after radiometric ages of Middle-Upper Ordovician (Sardic) granites.
STOP 7c. The Canigó granitic orthogneiss in the D6 road between Saorra and Pi: the Canigó gneiss derives from an Ordovician intrusive (462-471 Ma) and forms a 2000 m thick body with laccolithic morphology. A porhyritic rapakiwi texture is common in the G-2 type gneiss.

• 8th September – Fieldtrip to Mouthoumet massif, Occitanie.

STOP 8a. Surroundings of Montjoi village, Mouthoumet parauthochton: Lower Ordovician Davejean Volcanic Complex (rhyolitic tuffs) embedded in shales of the Davejean Group; Montjoi Formation with shale/limestone interbeds rich in echinoderms and brachiopods of late Katian age, unconformably overlain by the Marmairane Formation displaying unsorted siliciclastic strata (Hirnantian diamictites).

Base of the Lower-Ordovician Davejean Volcanosedimentary
Complex (here composed of rhyolitic tuffs) close to Montjoi.

STOP 8b. Marmaraine creek, close to Villerouge-Termenès, Félines-Palairac slice: Villerouge Formation with mafic lava and pyroclastic flows and laharic mudflows of tholeiitic affinity, capped by sandstones of the lower Katian Gascagne Formation and fossiliferous green shales of the Hirnantian Marmairane Formation.

• 9th September – Fieldtrip to Cabrières klippes, Montagne Noire, Occitanie.

STOP 9a. Rioberlou valley, Mont Peyroux nappe, southern flank: stratotype of the Cluse de l’Orb Formation (representative of the “Armorican Quartzite”-style sediments) sandwiched between the underlying La Maurerie Formation and the overlying Setso and Foulon formations, along the D14 road (between Roquebrun and Lugné).

STOP 9b. Landeyran valley, Mont Peyroux nappe, southern flank: fossiliferous shales of the Floian Landeyran Formation and angular discordance with Devonian “mur quartzeux”. Panorama from L’Escougoussou village and fossil sampling along the D-136 road.

Angular discordance of Floian Landeyran Formation and
Devonian "mur quartzeux" along the Landeyran valley.

Panorama of the Landeyran valley since L'Escougoussou
(Roquebrun, Hérault) seeing the angular discordance of
the Sardic Phase.

STOP 9c. Gorges d’Héric, Caroux Dome, Axial Zone: augen gneiss of the Somail Formation, rich in alkali feldspar and mica porphyroblasts, representative of metamorphic aureoles surrounding Sardic (Katian in age) granitoids.

Augen gneiss of the Katian Somail
Formation at Gorges d’Héric, Axial Zone.

STOP 9d. Grand Glauzy hill, Cabrières klippes, southern flank: Roque de Bandies Formation (polymictic and volcanosedimentary breccias capped by basaltic lava flows with tholeiitic affinity), Glauzy Formation (interbedded shales and fossiliferous sandstones forming two shallowing-upward sequences rich in brachiopods and trilobites, early Katian in age) and Gabian Formation (bryozoan and echinoderm-rich limestones and marlstones, late Katian in age), overlain by the Hirnantian erosive unconformity.